This research will investigate the crystal and molecular structures of various compounds of biological interest, including antibiotics, local anaesthetics, analgesic and compounds related to proteins and DNA. The aim is to determine, with a high degree of precision, the molecular dimensions of such substances in order that these data may be used in discussions of why and how they react as they do in living systems. This is a very complex area, but it will not be possible to understand fully the hows and the whys until sufficient structural data has become available. Particular attention will be paid to two very important structural features, namely, hydrogen bonding and conformations, especially at disulfide linkages. The work will make use of x-ray crystallographic methods, which involves the collection of thousands of diffraction maxima, finding suitable trial structures, and refining the hundreds of parameters by least-squares and electron density calculations.